Composition for cooling and lubricating a drive system of a vehicle

ABSTRACT

A composition with a kinematic viscosity for cooling and lubricating a drive system of an electric or hybrid vehicle, measured at 100° C. in accordance with the standard ASTM D445, in the range 3 to 10 mm 2 /s. The composition includes 70% to 90% of a base oil or a mixture of base oils having a kinematic viscosity, measured at 100° C. in accordance with the standard ASTM D445, of 1.5 to 8 mm 2 /s and selected from polyalphaolefins; and at least one thickening polymer.

The present invention relates to the field of compositions for lubricating and cooling a drive system of an electric or hybrid vehicle. In particular, it aims at proposing a composition endowed with both lubricating properties and with cooling properties for a drive system of an electric or hybrid vehicle, in particular for cooling and lubricating an electric motor.

Changes to international standards for the reduction of CO₂ emissions, but also for the reduction in energy consumption, is forcing vehicle manufacturers to propose alternative solutions to combustion engines.

One of the solutions identified by automobile manufacturers consists in replacing combustion engines by electric motors. Research into reducing CO₂ emissions have thus led to the development of electric vehicles by a certain number of car companies.

The term “electric vehicle” in the context of the present invention means a vehicle comprising an electric motor as the sole means of propulsion, in contrast to a hybrid vehicle that comprises a combustion engine and an electric motor as combined propulsion means.

The term “drive system” in the context of the present invention means a system comprising the mechanical parts necessary for the propulsion of an electric vehicle. The drive system thus more particularly encompasses an electric motor, a battery and possibly a transmission.

In general, in electric or hybrid vehicles, it is necessary to employ compositions which satisfy the dual constraints of cooling or lubricating the various parts of the drive system. These demands are typically satisfied by employing two distinct means, on the one hand lubricating compositions and cooling fluids on the other hand.

Thus, lubricating compositions, also known as “lubricants”, are routinely used in engines for the principal purposes of reducing frictional forces between the various metal parts that move in the engines. They are also effective in preventing premature wear or even damage to these parts, and in particular to their surfaces.

To this end, a lubricating composition is conventionally composed of one or more base oils that are generally associated with several additives intended to stimulate the lubricating performance of the base oils; friction modifiers are an example of such additives.

On another hand, electric motors generate heat during their operation. If the quantity of heat generated is greater than the quantity of heat normally dissipated into the environment, it is necessary to ensure that the engine is cooled. In general, cooling is carried out on one or more parts of the engine generating the heat and/or the parts of the engine which are sensitive to heat, in order to avoid reaching dangerous temperatures.

Traditionally, cooling electric motors with air is known, generally by means of forced convection. This cooling method has the advantage of avoiding having to prepare a specific cooling fluid. However, with the development of ever smaller engines with ever-increasing power, this cooling method is no longer sufficient, especially because of the limited efficiency of air for cooling.

Methods for cooling engines using water have also been proposed. Although the calorific capacity of water is high, it is not possible to envisage direct cooling by bringing the water into contact with the electric motor because of the electrical conductivity of water. Thus, the cooling system necessitates the use of an outer jacket, which considerably increases the volume of the engine.

Alternative methods for cooling an electric motor using a jet of oil have also been studied.

Liu et al. (EVS28, “Comparison of Thermal Performance between Direct Coil Cooling and Water Jacket Cooling for Electric Traction Motor based on Lumped parameter Thermal Network and Experimentation”, International Electric Vehicle Symposium and Exhibition) thus used analytical and experimental methods to compare the thermal performance of a conventional cooling system using water via an outer cooling jacket and that of a direct flow of oil for an electric traction motor.

Bennion et al. (“Convective Heat Transfer Coefficients of Automatic Transmission Fluid Jets with Implications for Electric Machine Thermal Management”, National Renewable Energy Laboratory) studied in more detail the parameters influencing the thermal transfer coefficients by convection for cooling carried out by a jet of an automatic transmission fluid (ATF) on surfaces that were representative of the wound coils of an electric motor.

WO 2011/113851 describes the use of a lubricating composition comprising a base oil, preferably a polyalphaolefin (PAO) or GTL, for cooling an electric motor of a hybrid vehicle or of a vehicle equipped with a kinetic energy recovery system (KERS). However, since the compositions described were optimized for engines for hybrid vehicles or for KERS systems, they will have insufficient cooling properties for deployment in an entirely electric drive system. In fact, an engine of an electric vehicle is subjected to much higher loads than an electric motor of a hybrid vehicle because of the much higher frequency of use, which implies the use of an oil with enhanced cooling properties.

The document EP 2 520 637 describes a lubricating composition comprising at least one ester or an ether for cooling an electric motor and for lubricating gears. However, esters are known to be unstable as regards oxidation. In addition, esters could give rise to problems with compatibility with the varnishes and seals routinely used in electric motors, which causes deterioration thereof. In particular, the winding of an electric motor is generally coated with a varnish. Because a lubricating composition is in direct contact with the winding, it is vital that the latter is inert as regards this varnish.

The document JP 2012/184360 may also be cited; it describes a lubricating composition comprising a synthetic base oil and a fluorinated compound for cooling an electric motor. However, the hydrochlorofluorocarbons present in those compositions are organic gases which have a large negative impact on the ozone layer and are powerful greenhouse gases. Fluorinated gases are also the subject of many regulations aimed at severely limiting their use.

At the present time, having regard to the limitations discussed above in respect of cooling compositions, the drive systems of electric vehicles proposed by the manufacturers are currently essentially cooled using air, water or compositions comprising water and a glycol.

For obvious reasons of economy and ease of use, it would be advantageous to have available a composition that could be used to simultaneously satisfy the requirements for lubrication and for cooling a drive system (motor, battery, etc.) of an electric or hybrid vehicle.

Unfortunately, at first sight, these two properties of lubrication and cooling suffer from opposing constraints. In fact, in order to cool an electric motor as best as possible, it is known to employ products such as water which are as fluid as possible. In point of fact, fluids of this type cannot be used to ensure a good level of lubrication. In contrast, compositions with a high viscosity that are capable of ensuring a good level of lubrication and protection of the members in contact against wear suffer from an unsatisfactory cooling potential.

Put precisely, the present invention aims to propose a novel composition that can simultaneously satisfy both of these functions, lubrication and cooling, while overcoming the disadvantages of the prior art.

More precisely, the inventors have discovered that it is possible to provide the dual function of lubrication and cooling by employing a mixture of a base formed by one or more oils selected from polyalphaolefins, which is far more fluid than known lubricating compositions, thickened by one or more specific polymers.

Hence, the present invention describes the use, for cooling and lubricating a drive system of an electric or hybrid vehicle, of a composition having a kinematic viscosity, measured at 100° C. in accordance with the standard ASTM D445, in the range 3 to 10 mm/s (cSt), and comprising at least:

-   -   a base oil or a mixture of base oils having a kinematic         viscosity, measured at 100° C. in accordance with the standard         ASTM D445, of 1.5 to 8.0 mm²/s; and     -   at least one thickening polymer selected from ester polymers;         linear or star, hydrogenated or non-hydrogenated homopolymers or         copolymers of styrene, butadiene and isoprene; polyacrylates;         linear or comb polymethacrylates; and olefin copolymers, in         particular ethylene/propylene copolymers.

In particular, in a first aspect, the present invention concerns the use, for cooling and lubricating a drive system of an electric or hybrid vehicle, of a composition having a kinematic viscosity, measured at 100° C. in accordance with the standard ASTM D445, in the range 3 to 10 mm²/s (cSt), and comprising at least:

-   -   70% to 90% by weight of base oil or a mixture of base oils         having a kinematic viscosity, measured at 100° C. in accordance         with the standard ASTM D445, of 1.5 to 8.0 mm²/s and selected         from polyalphaolefins; and     -   at least one thickening polymer selected from ester polymers;         linear or star, hydrogenated or non-hydrogenated homopolymers or         copolymers of styrene, butadiene and isoprene; polyacrylates;         linear or comb polymethacrylates; and olefin copolymers, in         particular ethylene/propylene copolymers.

Advantageously, a composition in accordance with the invention, employed in a drive system of an electric or hybrid vehicle, can be used to provide access to good properties both in terms of cooling and in terms of lubrication of the parts of a drive system.

More particularly, a composition in accordance with the invention may be used to cool and lubricate an electric motor of an electric or hybrid vehicle. It is particularly effective in cooling the power electronics and/or the rotor and/or the stator of an electric motor. It can also lubricate the bearings located between the rotor and the stator of an electric motor of an electric or hybrid vehicle.

Advantageously, a composition in accordance with the invention may be used to ensure lubrication of the transmission, when it is present, in particular the reduction gear, of an electric or hybrid vehicle.

In addition, a composition in accordance with the invention may advantageously be used to efficiently cool the battery present in an electric or hybrid vehicle.

Thus, advantageously, by using a single composition in accordance with the invention, it is possible, for example, to ensure both cooling of the battery and lubrication of the transmission, in particular of the reduction gear, in an electric or hybrid vehicle.

Advantageously, the composition is injected into the zones to be cooled under fairly high pressure, the resulting shear at the level of the injector advantageously being used to reduce the viscosity of the fluid at the level of the injection zone compared with the kinematic viscosity at rest, and thus to further increase the cooling potential of the composition.

In addition, a composition in accordance with the invention has the advantage of being easy to formulate. In addition to the combined properties of cooling and lubricating, it has good stability, in particular as regards oxidation, as well as good deaeration properties. Thus, the composition advantageously maintains its good cooling properties over time.

Advantageously, it also has good anticorrosion properties and can be used to limit the risks of deterioration of the seals or the varnish present in the drive system.

Finally, it complies with environmental and health standards.

The present invention also concerns a method for cooling and lubrication of a drive system of an electric or hybrid vehicle, comprising at least one step for bringing at least one mechanical part of said system into contact with a composition in accordance with the invention as described above.

Other characteristics, variations and advantages of employing a composition in accordance with the invention will become more apparent from the description, the examples and the figures below, given by way of non-limiting illustration of the invention.

FIG. 1 is a diagrammatic representation of a drive system of an electric or hybrid vehicle.

FIG. 2 is a graph representing the thermal properties of compositions in accordance with the invention, CL1 and CL2 (respectively • and +) and not in accordance with the invention, CC (▴), tested in accordance with Examples 1 and 2 below.

In the remainder of the text, the expressions “in the range to”, “from to” and “varying from to” are equivalent and are intended to signify that the limits are included, unless indicated otherwise.

Unless indicated otherwise, the expression “comprising a(n)” should be construed as meaning “comprising at least a(n)”.

Composition

As indicated above, a composition employed in accordance with the invention comprises at least:

-   -   70% to 90% by weight of a base oil or a mixture of base oils         with a kinematic viscosity, measured at 100° C. in accordance         with the standard ASTM D445, of 1.5 to 8.0 mm²/s and selected         from polyalphaolefins; and     -   one or more thickening polymers selected from ester polymers;         linear or star, hydrogenated or non-hydrogenated homopolymers or         copolymers of styrene, butadiene and isoprene; polyacrylates;         linear or comb polymethacrylates (PMA), and olefin copolymers,         in particular ethylene/propylene copolymers.

In the remainder of the text, the term “fluid base” will be used to designate the oil or the mixture of base oils having a kinematic viscosity, measured at 100° C. in accordance with the standard ASTM D445, of 1.5 to 8 mm²/s.

As discussed above, the combination of fluid base/thickening polymer(s) in accordance with the invention can be used to obtain a composition having good cooling properties, which are further enhanced by the effect of the shear applied at the injection level, while being consistent with a rheological behavior, in particular in terms of viscosity, which can procure good lubrication properties.

More particularly, a composition in accordance with the invention has a kinematic viscosity, measured at 100° C. in accordance with the standard ASTM D445, in the range 3 to 10 mm²/s, preferably in the range 3 to 9 mm²/s.

In particular, the composition employed is a non-Newtonian fluid.

In the present description, the term “Newtonian fluid” means a fluid for which there exists a linear relationship between the applied mechanical load (force exerted on the fluid per unit surface area) and the shear of the fluid (i.e. the speed gradient of the fluid). A “non-Newtonian fluid” is thus a fluid which is not a Newtonian fluid.

Base Oils

A composition in accordance with the invention employs a fluid base formed by one or more base oils, selected from polyalphaolefins and having a kinematic viscosity, measured at 100° C. in accordance with the standard ASTM D445, of 1.5 to 8 mm²/s, in particular 1.5 to 6.1 mm²/s, more particularly 1.5 to 4.1 mm²/s, yet more particularly 1.5 to 2.1 mm²/s.

In general, in the field of lubricants, base oils may be selected from oils of mineral or synthetic origins belonging to groups I to V of the classes defined in the API classification (or their equivalents in accordance with the ATIEL classification) and presented in Table A below, or mixtures thereof.

TABLE A Saturates Sulfur Viscosity content content index (VI) Group I  <90%  >0.03% 80 ≤ VI < 120 Mineral oils Group II ≥90% ≤0.03% 80 ≤ VI < 120 Hydrocracked oils Group III ≥90% ≤0.03% ≥120 Hydrocracked oils or hydroisomerized oils Group IV Polyalphaolefins (PAO) Group V Esters and other bases not included in groups I to IV

The mineral base oils include all types of base oils obtained by atmospheric and vacuum distillation of crude oil, followed by refining operations such as solvent extraction, deasphalting, solvent dewaxing, hydrotreatment, hydrocracking, hydroisomerization and hydrofinishing.

Mixtures of synthetic and mineral oils may also be employed.

The lubricating bases employed to produce the compositions in accordance with the invention must also satisfy the viscosity criterion cited above, must have properties, in particular the viscosity index, sulfur content or resistance to oxidation, which are adapted to use for the drive systems of an electric or hybrid vehicle.

The base oils may also be selected from synthetic oils, such as certain esters of carboxylic acids and alcohols, and from polyalphaolefins (PAO).

The oil or the base oils of a composition employed in accordance with the invention are selected from polyalphaolefins (PAO). The PAOs used as base oils are, for example, obtained from monomers containing 4 to 32 carbon atoms, for example from octene or decene.

The mass average molecular mass of the PAO can vary relatively widely. Preferably, the mass average molecular mass of the PAO is less than 600 Da. The mass average molecular mass of the PAO may also be from 100 to 600 Da, from 150 to 600 Da, or in fact from 200 to 600 Da.

As an example, the PAOs employed in the context of the invention, having a kinematic viscosity, measured at 100° C. in accordance with the standard ASTM D445, of 1.5 to 8 mm²/s, are commercially available from Ineos under the trade names Durasyn® 162, Durasyn® 164, Durasyn® 166 and Durasyn® 168.

In accordance with a particular embodiment, a composition employed in accordance with the invention is free from polyalkylene glycol (PAG) obtained by polymerization or copolymerization of alkylene oxides containing 2 to 8 carbon atoms, in particular 2 to 4 carbon atoms.

In accordance with a particular embodiment, the fluid base of a composition employed in accordance with the invention comprises a content that is strictly less than 30% by weight of ester and ether type base oils, in particular less than 25% by weight of ester and ether type base oils, in particular less than 10% by weight.

In particular, the fluid base of a composition employed in accordance with the invention is free from ester type oils.

Preferably, a composition employed in accordance with the invention comprises a fluid base formed by one or more base oils having a kinematic viscosity, measured at 100° C. in accordance with the standard ASTM D445, in the range 1.5 and 8 mm²/s.

In other words, a composition of the invention may, for example, be free from base oil or a mixture of base oils not satisfying the criterion regarding the kinematic viscosity, measured at 100° C. in accordance with the standard ASTM D445, in particular free from an oil or mixture of base oils having a viscosity of more than 9 mm²/s.

It is within the purview of the person skilled in the art to adjust the fluid base content to be employed in a composition in accordance with the invention in order to obtain the desired viscosity for the composition.

As indicated above, the fluid base provides the cooling potential of the composition employed in accordance with the invention. In particular, the fluidity of the base ensures the good cooling properties when the composition is employed for a drive system of an electric or hybrid vehicle.

The cooling properties of the composition employed are more advantageously increased by the shear applied to the composition at the level of injection, which brings the fluid to a level of viscosity which is lower than when at rest. Thus, advantageously, the impact of employing thickening polymers in accordance with the invention on the cooling capacity of the composition is under control.

A lubricating composition may comprise 60% to 90% by weight of base oil or a mixture of base oils having a kinematic viscosity, measured at 100° C. in accordance with the standard ASTM D445, of 1.5 to 8 mm²/s with respect to the total weight of the composition.

More particularly, a composition employed in accordance with the invention comprises 70% to 90% by weight, preferably 80% to 90% by weight, of base oil or a mixture of base oils having a kinematic viscosity, measured at 100° C. in accordance with the standard ASTM D445, of 1.5 to 8 mm²/s with respect to the total weight of the composition.

Thickening Polymers

A composition used in accordance with the invention furthermore comprises one or more polymers, known as thickening polymers.

The polymer or polymers are selected for their capacity to thicken the fluid base in accordance with the invention in order to provide the desired lubrication properties for the composition.

The thickening polymers in accordance with the invention may in particular be selected from polymers known as “viscosity index improvers” (VI).

Viscosity improving polymers of this type have been described, for example, in the documents WO 9418288, EP 2 363 454, EP 2 164 885, EP 0 699 694, WO 2007/003238 and WO 2007/025837.

It should be understood that the thickening polymer or polymers are distinct from the oil or said base oils as described above.

In particular, they may be polymers selected from ester polymers; linear or star, hydrogenated or non-hydrogenated homopolymers or copolymers of styrene, butadiene and isoprene; polyacrylates; linear or comb polymethacrylates, and olefin copolymers, in particular ethylene/propylene copolymers.

Preferably, the thickening polymer may more particularly be selected from linear or comb polymethacrylates, linear or hydrogenated star copolymers of styrene, butadiene and isoprene, and their mixtures.

Advantageously, the thickening polymer may more particularly be selected from comb polymethacrylates, hydrogenated star copolymers of styrene, butadiene and isoprene, and their mixtures.

As an example, the polymethacrylate comb polymers within the meaning of the invention are described in the patent applications EP 2 164 885, EP 0 699 694, WO 2007/003238 and WO 2007/025837; and the structures and definitions of these polymers as described in those documents are hereby incorporated into the description of the present application.

Examples of polymethacrylate comb polymers within the meaning of the invention are commercially available from Evonik under the trade name Viscoplex® 3-200.

By way of another example, the hydrogenated star copolymers of styrene, butadiene and isoprene within the meaning of the invention are described in the patent application EP 2 363 454 and the structures and definitions of these polymers as described in EP 2 363 454 are hereby incorporated into the description of the present application.

Examples of hydrogenated star copolymers of styrene, butadiene and isoprene within the meaning of the invention are sold by Infineum under the trade name SV® 261.

Using thickening polymer(s) ensures that the composition will thicken sufficiently to ensure, when it is employed for a drive system of an electric or hybrid vehicle, an anti-wear level of protection, i.e. of lubrification, which is satisfactory, without in any way affecting the cooling potential of the composition.

In particular, the thickening polymer(s) content in a composition in accordance with the invention is 0.5% to 10% by weight, with respect to the total weight of the composition, preferably 1% to 8% by weight, more preferably 1.5% to 5% by weight.

This quantity means the quantity of active material of the polymer. In fact, the polymer used in the context of the present invention may be in the form of a dispersion in one or more mineral or synthetic oil(s).

Particularly again, a composition used in accordance with the invention may comprise 1% to 25% by weight, preferably 2% to 20% by weight, more preferably 4% to 20% by weight of thickening polymer(s) diluted in one or more base oil(s), with respect to the total weight of the composition.

It is within the purview of the person skilled in the art to adjust the proportions of the various constituents of the composition, in particular of the fluid base and of the thickening polymers, in order to obtain the viscosity required in accordance with the invention.

In accordance with a particular embodiment, a composition used in accordance with the invention comprises at least one base oil selected from PAOs and at least one polymer selected from comb polymethacrylates, hydrogenated star copolymers of styrene, butadiene and isoprene, and their mixtures.

In particular, when the base oil is selected from PAOs, in a composition used in accordance with the present invention, it is associated with at least one polymer selected from comb polymethacrylates.

Particularly again, when the base oil is selected from PAOs, in a composition used in accordance with the present invention, it is associated with at least one polymer selected from hydrogenated star copolymers of styrene, butadiene and isoprene.

In accordance with one variational embodiment, a composition employed in accordance with the invention is formed, in other words consists of, a mixture:

-   -   of a base oil, or mixture of base oils, having a kinematic         viscosity, measured at 100° C. in accordance with the standard         ASTM D445, of 1.5 to 8 mm²/s; and     -   of one or more thickening polymers as defined above.

Preferably, a composition employed in accordance with the invention is formed:

-   -   from one or more base oils having a kinematic viscosity,         measured at 100° C. in accordance with the standard ASTM D445,         of 1.5 to 8 mm²/s; and     -   from one or more thickening polymers as defined above.

Alternatively, a composition that is employed may furthermore comprise one or more additives as defined more precisely in the text below.

Additives

The additives that may be incorporated into a composition in accordance with the invention may be selected from friction modifiers, detergents, anti-wear additives, extreme pressure additives, dispersants, antioxidants, pour point improvers, anti-foaming agents and their mixtures.

It should be understood that the nature and the quantity of the additives employed are selected in a manner such as not to affect the combined properties of lubrication and cooling power of the composition of the invention.

These additives may be introduced in isolation and/or in the form of a mixture reflecting those already on sale for commercial lubricant formulations for vehicle engines with a performance level as defined by the ACEA (Association des Constructeurs Européens d′Automobiles) [European Automobile Manufacturers Association] and/or the API (American Petroleum Institute), which are well known to the person skilled in the art.

The anti-wear additives and the extreme pressure additives protect the frictional surfaces by forming a protective film adsorbed onto those surfaces.

A wide variety of anti-wear additives exists. Preferably, for the lubricating composition in accordance with the invention, the anti-wear additives are selected from phospho-sulfur additives such as metallic alkylthiophosphates, in particular zinc alkylthiophosphates, and more specifically zinc dialkyldithiophosphates, or ZnDTP. The preferred compounds have the formula Zn((SP(S)(OR²)OR³))₂, in which R² and R³, which may be identical or different, independently represent an alkyl group, preferably an alkyl group containing 1 to 18 carbon atoms.

Amine phosphates are also anti-wear additives that can be employed in a composition in accordance with the invention. However, the phosphorus supplied by these additives may act as a poison for the catalytic systems of automobiles, because these additives are ash generators. These effects can be minimized by partially substituting the amine phosphates by additives which do not supply phosphorus such as, for example, polysulfides, in particular sulfur-containing olefins.

A composition used in accordance with the invention may comprise 0.01% to 6% by weight, preferably 0.05% to 4% by weight, more preferably 0.1% to 2% of anti-wear additives and extreme pressure additives, by weight with respect to the total weight of the composition.

In accordance with a particular embodiment, a composition used in accordance with the invention is free from anti-wear additives and extreme pressure additives. In particular, a composition used in accordance with the invention is advantageously free from phosphorus-containing additives.

A composition used in accordance with the invention may comprise at least one friction-modifying additive. The friction-modifying additive may be selected from a compound supplying metallic elements and a compound that is free from ash. Examples of compounds supplying metallic elements that may be cited are complexes of transition metals such as Mo, Sb, Sn, Fe, Cu, Zn; the ligands of these may be hydrocarbon compounds containing oxygen, nitrogen, sulfur or phosphorus atoms. The anti-wear additives that are free from ash are generally of organic origin and may be selected from monoesters of fatty acids and polyols, alkoxylated amines, alkoxylated fatty amines, fatty epoxy compounds, fatty epoxy compounds of borate, fatty amines or fatty acid glycerol esters. In accordance with the invention, the fatty compounds comprise at least one hydrocarbon group containing 10 to 24 carbon atoms.

A composition used in accordance with the invention may comprise 0.01% to 2% by weight or 0.01% to 5% by weight, preferably 0.1% to 1.5% by weight or 0.1% to 2% by weight of anti-wear additive, with respect to the total weight of the composition.

Advantageously, a composition in accordance with the invention is free from anti-wear additives.

A composition used in accordance with the invention may comprise at least one antioxidant additive.

The antioxidant additive can in general retard the degradation of the composition when in service. This degradation may in particular be manifested by the formation of deposits, the presence of sludge or an increase in the viscosity of the composition.

In particular, antioxidant additives act as radical inhibitors or hydroperoxide destroyers. Examples of antioxidant additives in routine use that may be cited are antioxidant additives of the phenol type, antioxidant additives of the amine type, and phosphosulfur antioxidant additives. Certain of these antioxidant additives, for example phosphosulfur antioxidant additives, may be generators of ash. Phenolic antioxidant additives may be free from ash or in fact be in the form of neutral or basic metallic salts. The antioxidant additives may in particular be selected from sterically hindered phenols, sterically hindered phenol esters and sterically hindered phenols comprising a thioether bridge, diphenylamines, diphenylamines substituted with at least one C₁-C₁₂ alkyl group, N,N′-dialkylaryldiamines and their mixtures.

Preferably in accordance with the invention, the sterically hindered phenols are selected from compounds comprising a phenol group wherein at least one vicinal carbon of the carbon carrying the alcohol function is substituted with at least one C₁-C₁₀ alkyl group, preferably a C₁-C₆ alkyl group, preferably a C₄ alkyl group preferably by the tert-butyl group.

Amine compounds are another class of antioxidant additives that may be used, optionally in combination with phenolic antioxidant additives. Examples of amine compounds are aromatic amines, for example aromatic amines with formula NR⁴R⁵R⁶, in which R⁴ represents an aliphatic group or an aromatic group, which may be substituted, R⁵ represents an aromatic group, which may be substituted, R⁶ represents a hydrogen atom, an alkyl group, an aryl group or a group with formula R⁷S(O)_(z)R⁸, in which R⁷ represents an alkylene group or an alkenylene group, R⁸ represents an alkyl group, an alkenyl group or an aryl group, and z represents 0, 1 or 2.

Sulfur-containing alkyl phenols or their salts of alkali and alkaline-earth metals may also be used as antioxidant additives.

Another class of antioxidant additives is that of copper-containing compounds, for example copper thiophosphates or dithiophosphates, salts of copper and carboxylic acids, dithiocarbamates, sulfonates, phenates, copper acetylacetonates. Copper I and II salts and salts of succinic acid or anhydride may also be used.

A composition used in accordance with the invention may contain any type of antioxidant additive known to the person skilled in the art.

Advantageously, a composition used in accordance with the invention comprises at least one antioxidant additive that is free from ash.

A composition used in accordance with the invention may comprise 0.5% to 2% by weight of at least one antioxidant additive, with respect to the total weight of the composition.

A composition used in accordance with the invention may also comprise at least one detergent additive.

Detergent additives can generally be used to reduce the formation of deposits on the surface of metallic parts by dissolving secondary oxidation and combustion products.

The detergent additives that may be used in a composition used in accordance with the invention are generally known to the person skilled in the art. The detergent additives may be anionic compounds comprising a long lipophilic hydrocarbon chain and a hydrophilic head. The associated cation may be a metallic cation of an alkali or alkaline-earth metal.

The detergent additives are preferably selected from the alkali metal or alkaline-earth metal salts of carboxylic acids, sulfonates, salicylates, naphthenates, as well as the salts of phenates. The alkali and alkaline-earth metals are preferably calcium, magnesium, sodium or barium.

These metallic salts generally comprise the metal in a stoichiometric quantity or in fact in excess, i.e. in a quantity that is greater than stoichiometric quantities. Thus, they are overbased detergent additives; the metal in excess providing the overbased nature of the detergent additive is then generally in the form of a metallic salt that is insoluble in oil, for example a carbonate, a hydroxide, an oxalate, an acetate, or a glutamate, preferably a carbonate.

A composition used in accordance with the invention may, for example, comprise 2% to 4% by weight of detergent additive with respect to the total weight of the composition.

A composition used in accordance with the invention may also comprise at least one additive that reduces the pour point.

By slowing down the formation of crystals of paraffin, the pour point-reducing additives generally improve the cold behavior of the composition.

Examples of additives that reduce the pour point that may be cited are alkyl polymethacrylates, polyacrylates, polyarylamides, polyalkylphenols, polyalkylnaphthalenes, and alkyl polystyrenes.

In addition, a composition used in accordance with the invention may comprise at least one dispersing agent.

The dispersing agent may be selected from Mannich bases, succinimides and their derivatives.

A composition used in accordance with the invention may, for example, comprise 0.2% to 10% by weight of dispersing agent with respect to the total weight of the composition.

Application

As indicated above, because of its combined properties in terms of cooling and lubrication, a composition as described above may be employed both as a lubricant and as a cooling fluid for a drive system of an electric or hybrid vehicle.

In particular, the invention concerns the use of a composition as defined above for cooling and lubricating an electric motor of an electric or hybrid vehicle, and its various parts, in particular moving parts. The invention is also applicable to the battery of an electric or hybrid vehicle.

As shown diagrammatically in FIG. 1, the drive system of an electric or hybrid vehicle in particular comprises the electric motor portion (1). This typically comprises power electronics (11) connected to a stator (13) and a rotor (14).

The stator comprises coils, in particular copper coils, which are supplied with alternating electric current. This can generate a rotating magnetic field. The rotor per se comprises coils, permanent magnets or other magnetic materials, and is caused to rotate by the rotating magnetic field.

The power electronics (11), the stator (13) and the rotor (14) of an electric motor (1) are parts with complicated structures and generate a large quantity of heat during operation of the motor. Thus, it is vital to provide cooling for the electric motor, in particular of the power electronics.

In addition, the bearing (12), generally integrated between the stator (13) and the rotor (14), is subjected to high mechanical loads and problems arise with wear by fatigue. Thus, it is necessary to lubricate the bearing in order to increase its service life.

The composition employed in accordance with the invention as described above can be used to provide, inside an electric or hybrid vehicle, both the function of lubrication and of protection of the members in contact against wear, and the function of cooling.

Hence, the invention in particular concerns the use of a composition as described above to cool and lubricate an electric motor of an electric or hybrid vehicle.

In particular, it can be used to cool the power electronics and/or the rotor and/or the stator of the electric motor. It can also carry out lubrication of the bearings located between the rotor and the stator of an electric motor of an electric or hybrid vehicle.

A drive system of an electric or hybrid vehicle may also comprise a transmission, and in particular a speed reduction gear (3) that can be used to reduce the rate of rotation at the output of the electric motor and adapt the speed transmitted to the wheels, thus allowing the speed of the vehicle to be controlled at the same time.

This reduction gear is subjected to high frictional loads, and thus has to be lubricated in an appropriate manner in order to prevent it from being damaged too quickly.

Thus, the invention also concerns the use of a composition as described above for lubrication of the transmission, in particular the reduction gear, in an electric or hybrid vehicle.

Advantageously, a composition in accordance with the invention may thus be used to lubricate and cool both the electric motor and the transmission, in particular the reduction gear, in an electric or hybrid vehicle.

As mentioned above, the electric motor is typically powered by an electric battery (2). Lithium ion batteries are the most widespread in the field of electric vehicles. The development of ever more powerful batteries and with a size that is ever more reduced implies that problems will arise with cooling this battery. In fact, as soon as the battery exceeds temperatures of the order of 50° C. to 60° C., there is a high risk of ignition, or even of explosion, of the battery. There is also a need to maintain the battery at a temperature of more than approximately 20° C. to 25° C. in order to prevent the battery from discharging too rapidly and in order to prolong its service life.

Thus, a composition of the invention may be employed in order to cool the battery of an electric or hybrid vehicle.

It should be understood that the uses described above may be combined; a composition as described above may be used both as a lubricant and as a cooling fluid for the engine, the battery and the transmission of an electric or hybrid vehicle.

Thus, the invention has the advantage of enabling a single composition that associates the properties of lubrication and of cooling to be employed as a lubricant and as a cooling fluid in an electric or hybrid vehicle.

The invention also concerns a method for cooling and for lubricating a drive system of an electric or hybrid vehicle, comprising at least one step for bringing at least one mechanical part of an electric motor and/or battery and/or transmission into contact with a composition as defined hereinabove.

The set of characteristics and preferences described for the composition used in accordance with the invention as well as for its uses also apply to this method.

Cooling with a composition used in accordance with the invention may be carried out using any method that is known to the person skilled in the art.

Examples of direct use that may be cited are jet cooling, spray cooling or in fact by forming a mist from the composition in accordance with the invention under pressure and under gravity, in particular on the winding of the rotor and/or the stator.

Advantageously, the composition is injected, using a jet under a fairly high pressure, into the zones of the drive system to be cooled as described, for example, in the publications by Liu et al. and Bennion et al. cited above. Advantageously, the shear resulting from this injection can be used to reduce the viscosity of the fluid at the level of the injection zone, compared with the kinematic viscosity at rest, and thus of further increasing the potential cooling of the composition.

In addition, the oil circulation systems in current use in electric motors may be employed as described, for example, in the document WO 2015/116496.

In accordance with the invention, the particular characteristics, advantages or preferences of the composition in accordance with the invention can be used to define the uses in accordance with the invention which are also particular, advantageous or preferred.

The invention will now be described with the aid of the following examples given, of course, by way of non-limiting illustration of the invention.

EXAMPLES Example 1

Preparation of Lubricating Compositions in Accordance with the Invention (CL) and of Comparative Compositions (CC)

The various components of the compositions were mixed as a function of the nature and the quantities of the products (expressed as a percentage by weight) as shown in Table 1 below.

TABLE 1 CL1 CL2 CC1 PAO having a kinematic viscosity, measured at 84.0 87.0 0 100° C. in accordance with the standard ASTM D445, of 1.5 to 2.1 mm²/s PAO having a kinematic viscosity, measured at 0 0 40 100° C. in accordance with the standard ASTM D445, of 3.8 to 4.1 mm²/s PAO having a kinematic viscosity, measured at 0 0 60 100° C. in accordance with the standard ASTM D445, of 7.7 to 8.0 mm²/s Polymethacrylate comb polymer ⁽¹⁾ 16.0 0 0 Hydrogenated star copolymer of butadiene- 0 13.0 0 styrene-isoprene⁽²⁾ ⁽¹⁾ Polymethacrylate comb polymer commercially available from Evonik under the trade name Viscoplex ® 3-200; ⁽²⁾Star hydrogenated copolymer of styrene, butadiene and isoprene sold by Infineum under the trade name SV ® 261.

The characteristics of the compositions prepared in this manner are presented in Table 2.

TABLE 2 CL1 CL2 CC1 KV100 - ISO 3104 (mm² · s⁻¹)* 6.10 5.95 5.90 *kinematic viscosity measured at 100° C. in accordance with the standard ISO 3104

Example 2

Measurement of Thermal Properties of Compositions in Accordance with the Invention

One way in which to measure the thermal properties of a fluid consists of measuring the heat exchange coefficient of the fluid (thermal transfer per unit of surface area and temperature). A fluid with a higher thermal exchange coefficient has better cooling properties.

A test for measuring the thermal exchange coefficient of each of the compositions described in Table 1 was carried out.

The principle of the test consisted of projecting a jet of oil with the aid of a spray nozzle perpendicular to a metal plate heated by induction. A thermal camera placed above the plate records the temperature profile during projection of the oil. From the values for the variation of the temperature over the plate, it is then possible to calculate the mean thermal exchange coefficient of the composition.

It is possible to vary different parameters, in particular the temperature of the plate, the size of the spray nozzle and the pressure at which the oil is projected. The measurement of the thermal coefficient is carried out at different distances from the impact point of the jet on the metal plate, this distance corresponding to the radius. The test conditions are described in Table 3 below.

TABLE 3 Characteristic Unit Value Temperature ° C. 80-140   Pressure bar 10 Radius mm 0-0.016

The results obtained are shown in the graph of FIG. 2.

The various temperatures (in degrees Celsius) detected on the heated plate are shown along the ordinate; and the radii corresponding to the various distances (in meters) from the point of impact of the jet on the metal plate are shown along the abscissa.

It can be seen from FIG. 2 that after a radius of 0.01 m, there is a significant difference of at least 5° C. between the temperatures detected on the heated plate onto which the compositions of the invention (CL1, • and CL2, +) and the comparative composition (CC1, ▴) have respectively been projected.

This therefore implies that the compositions in accordance with the invention can cool the heated plate better and maintain a stable temperature compared with the comparative compositions not comprising a thickening polymer.

As a consequence, the compositions in accordance with the invention can not only be used to lubricate, but also to cool a drive system of an electric or hybrid vehicle. 

1. A method for cooling and lubricating a drive system of an electric or hybrid vehicle, comprising at least a step of bringing at least one mechanical part of said system into contact with a composition having a kinematic viscosity, measured at 100° C. in accordance with the standard ASTM D445, in the range 3 to 10 mm²/s (cSt), and comprising at least: 70% to 90% by weight of base oil, or a mixture of base oils, having a kinematic viscosity, measured at 100° C. in accordance with the standard ASTM D445, of 1.5 to 8 mm²/s and selected from polyalphaolefins; and at least one thickening polymer selected from ester polymers; linear or star, hydrogenated or non-hydrogenated homopolymers or copolymers of styrene, butadiene and isoprene; polyacrylates; linear or comb polymethacrylates; and olefin copolymers.
 2. The method as claimed in claim 1, wherein composition having a kinematic viscosity, measured at 100° C. in accordance with the standard ASTM D445, is in the range 3 to 9 mm²/s.
 3. The method as claimed in claim 1, wherein the thickening polymer or polymers are selected from comb polymethacrylates, hydrogenated star copolymers of styrene, butadiene and isoprene, and their mixtures.
 4. The method as claimed in claim 1, wherein the composition comprises 0.5% to 10% by weight of thickening polymer(s) with respect to the total weight of the composition.
 5. The method as claimed in claim 1, said composition further comprises at least one additive selected from friction modifiers, detergents, anti-wear additives, extreme pressure additives, dispersants, antioxidants, pour point improvers, anti-foaming agents and their mixtures.
 6. The method as claimed in claim 1, for cooling and lubricating an electric motor of an electric or hybrid vehicle.
 7. The method as claimed in claim 6, for cooling the power electronics and/or the rotor and/or the stator of an electric motor.
 8. The method as claimed in claim 6, for lubricating the bearings located between the rotor and the stator of an electric motor.
 9. The method as claimed in claim 1, for cooling the battery of an electric or hybrid vehicle.
 10. The method as claimed in claim 1, for lubricating the transmission of an electric or hybrid vehicle.
 11. The method as claimed in claim 1, said composition comprising 1.5% to 5% by weight of thickening polymer(s) with respect to the total weight of the composition.
 12. The method as claimed in claim 10, for lubricating the reduction gear of an electric or hybrid vehicle. 